The isothermal corrosion tests of several types of stainless steels, Ni-based alloys, and ferritic-martensiticsteels (FMS) were carried out at the temperature of 550 and 650 oC in SFR S-CO2 environment (200 bar)for 1000 h. The weight gain was greater in the order of FMSs, stainless steels, and Ni-based alloys. Forthe FMSs (Fe-based with low Cr content), a thick outer Fe oxide, a middle (Fe,Cr)-rich oxide, and aninner (Cr,Fe)-rich oxide were formed. They showed significant weight gains at both 550 and 650 oC. Inthe case of austenitic stainless steels (Fe-based) such as SS 316H and 316LN (18 wt.% Cr), the corrosionresistance was dependent on test temperatures except SS 310S (25 wt.% Cr). After corrosion test at 650oC, a large increase in weight gain was observed with the formation of outer thick Fe oxide and inner(Cr,Fe)-rich oxide. However, at 550 oC, a thin Cr-rich oxide was mainly developed along with partiallydistributed small and nodular shaped Fe oxides. Meanwhile, for the Ni-based alloys (16-28 wt.% Cr), avery thin Cr-rich oxide was developed at both test temperatures. The superior corrosion resistance of highCr or Ni-based alloys in the high temperature S-CO2 environment was attributed to the formation of thinCr-rich oxide on the surface of the materials.